title: Smac mimetics activate the E3 ligase activity of cIAP1 protein by promoting RING domain dimerization.
abstract: The inhibitor of apoptosis (IAP) proteins are important ubiquitin E3 ligases that regulate cell survival and oncogenesis. The cIAP1 and cIAP2 paralogs bear three N-terminal baculoviral IAP repeat (BIR) domains and a C-terminal E3 ligase RING domain. IAP antagonist compounds, also known as Smac mimetics, bind the BIR domains of IAPs and trigger rapid RING-dependent autoubiquitylation, but the mechanism is unknown. We show that RING dimerization is essential for the E3 ligase activity of cIAP1 and cIAP2 because monomeric RING mutants could not interact with the ubiquitin-charged E2 enzyme and were resistant to Smac mimetic-induced autoubiquitylation. Unexpectedly, the BIR domains inhibited cIAP1 RING dimerization, and cIAP1 existed predominantly as an inactive monomer. However, addition of either mono- or bivalent Smac mimetics relieved this inhibition, thereby allowing dimer formation and promoting E3 ligase activation. In contrast, the cIAP2 dimer was more stable, had higher intrinsic E3 ligase activity, and was not highly activated by Smac mimetics. These results explain how Smac mimetics promote rapid destruction of cIAP1 and suggest mechanisms for activating cIAP1 in other pathways.
authors.affiliation: Department of Biochemistry, La Trobe University, Victoria 3086, Australia.
authors.forename: Rebecca
authors.initials: R
authors.lastname: Feltham
authors.forename: Bodhi
authors.initials: B
authors.lastname: Bettjeman
authors.forename: Rhesa
authors.initials: R
authors.lastname: Budhidarmo
authors.forename: Peter D
authors.initials: PD
authors.lastname: Mace
authors.forename: Sarah
authors.initials: S
authors.lastname: Shirley
authors.forename: Stephen M
authors.initials: SM
authors.lastname: Condon
authors.forename: Srinivas K
authors.initials: SK
authors.lastname: Chunduru
authors.forename: Mark A
authors.initials: MA
authors.lastname: McKinlay
authors.forename: David L
authors.initials: DL
authors.lastname: Vaux
authors.forename: John
authors.initials: J
authors.lastname: Silke
authors.forename: Catherine L
authors.initials: CL
authors.lastname: Day
mesh_terms: D000818:Animals; D017209:Apoptosis; D032701:Biomimetics; D002942:Circular Dichroism; D019281:Dimerization; D004789:Enzyme Activation; D006801:Humans; D051034:Inhibitor of Apoptosis Proteins / Q000737:chemistry* / Q000378:metabolism*; D016086:Lentivirus / Q000235:genetics; D051379:Mice; D016296:Mutagenesis; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D012542:Scattering, Radiation; D015398:Signal Transduction; D025801:Ubiquitin / Q000737:chemistry; D044767:Ubiquitin-Protein Ligases / Q000378:metabolism*
chemical_list: D051034:Inhibitor of Apoptosis Proteins; D025801:Ubiquitin; D044767:Ubiquitin-Protein Ligases